Code Division Multiple Access (“CDMA”) is a digital technology commonly used in wireless communication systems. In a CDMA system, a CDMA device, such as a base station, transmits a CDMA signal to numerous communication devices, such as wireless CDMA handsets. CDMA is a “spread spectrum” technology that assigns a unique code to all bits, transmits a scrambled CDMA signal of encoded bits, and reassembles the bits in their original format.
In a CDMA signal, the individual calls are not separated based on frequency or time, but are spread across an entire frequency band. Each individual call is encoded with a unique pseudo random sequence. The CDMA device then combines the encoded signals together to form a radio frequency (“RF”) CDMA signal. The receiving communication device uses the unique pseudo random sequence to derive and receive a particular call.
CDMA systems utilize orthogonal and pseudo orthogonal sequences in order to simultaneously carry a plurality of channels. Each channel requires power to transmit its bit stream, which also generates noise for other channels in the same band. Therefore, the power level of any bit stream has a direct impact on the system's capacity and the system is said to be interference limited.
To prevent operation above a maximum power level during high traffic periods, CDMA devices utilize call-blocking technology. Call-blocking technology is initiated during high traffic periods to limit the number of calls processed by the CDMA device. During periods where call blocking is initiated, at least a portion of new calls are blocked to maintain current traffic loads and channel power that result in system operation at or below the maximum power level. Such call-blocking, however, is generally undesirable as it has the obvious disadvantage of dissatisfied customers.
One solution to mitigate the problem of blocking calls during high traffic periods is to adjust the bit rate allocated to calls based on the current voice activity over the CDMA device. The method works by allocating a lower bit rate to voice calls during higher or peak traffic periods, and allocating a higher or standard bit rate during lower or off peak traffic periods. This permits the CDMA device to accommodate more calls before call blocking is implemented. Unfortunately, this method automatically lowers bit rate allocations to calls regardless of other factors for the call, such as class of service.